Bryant plus 90 problems

[danus5]

I have a bryant 90 percent eff. furnance that fails to make heat. The fans run but no heat. This is random it may run for weeks with out a problem. We have had three sevicemen out to check it and no luck. There is an adjustable air cap on the intake blower that they have completely removed to give it more air. no change. then they suggested the 2" pipe was to small, so i changed to 3" still no change. They have no clue. It seems to be flashing a code 31, (three short pulses and one long). Sticking pressure valve?
Any help would be great!

[hvacwiz]

your right, code 31 is a presure switch fault. have they replaced entire flue pipe or just a portion of the pipe, there could be a bird or bee nest in the flue that wont allow the switch to pull in. Also things to check are you presure switch hose to make sure there are no cracks and the collector box where the tube connects to could also be resticted or you could simply have a faulty presure switch that needs replaced. Also make sure your condensate trap and drain are not plugged. GoodLuck

[danus5]

Yes we changed the entire flue. I tapped the pressure switch and it fired right up. I definately will check the other things you suggested to make sure things are what they should be.

Thanks

[hvacwiz]

If you tapped the pressure switch and it fired right up, I would change the switch, I have a hunch that will take care of your problem.